Floodplain maps

King County, Washington

FEMA is updating flood maps throughout King County based on new data about flood hazards. This is the first update in many years and is an important opportunity for our region to get a better and more accurate assessment of the flood hazards we face.

If you have questions about the flood map updates, please contact the River and Floodplain Management Section at 206-477-4727. If you’d like to view an interactive map of the preliminary flood maps, you can view that here.

If you would like to have a flood map of your specific property to bring to the meetings, please email floodmapquestions@kingcounty.gov and it will be emailed to you. Please include your full name, full property address, parcel number (if available), contact information (including mailing address, email address, and phone number), and questions or specific requests.

Staff from the River and Floodplain Management Section can assist with the following flood map information by calling 206-477-4727.

Confirming if a property is located within a FEMA mapped Special Flood Hazard Area (SFHA), or flood prone area identified by King County.

Provide FEMA elevation certificates if available. King County has elevation certificates for many properties within the SFHA.

Determine what regulatory provisions may apply to a specific property.

If available, provide information on past flood damage to a property.

Development in Floodplains

All development in a mapped floodplain needs a permit, and buildings, in particular, must demonstrate compliance with King County Code. Managing development in floodplains is a core responsibility of King County as part of our participation in the National Flood Insurance Program. Proper permitting means that flood insurance will remain available to all residents of unincorporated King County.

Floodplain development standards are part of the Critical Areas chapter of King County Code 21A.24. Sections 21A.24.230 through 21A.24.272 establish the requirements for floodplains, including coastal high hazard areas. Some of the key pieces of floodplain development standards are the following requirements:

New or substantially improved homes be elevated to 3 feet above the 100-year flood elevation.

No development will occur in areas where the 100-year flood depths are greater than 3 feet and where the velocity of floodwaters are greater than 3 feet per second.

Development in the floodway will provide certification that it will not cause a rise in 100-year flood elevations for any other property.

Any development that includes fill will provide compensatory storage to offset the loss in flood storage.

In coastal flood hazard zones, buildings are only allowed to be built on piers or posts.

All buildings must have a FEMA Elevation Certificate completed by a licensed surveyor that shows compliance with the King County Code.